In petroleum refining, the crude oil systems employed as feedstocks are prone to produce material that deposits and accumulates upon the surfaces of heat transfer equipment contacted therewith resulting in the fouling of petroleum process equipment. In normal, continuous use, for example, the heat exchangers used in almost all crude oil unit processes suffer gradually increasing losses in efficency, heat transfer, and throughput owing to deposition of material on the inner surfaces thereof. Consequently, crude oil process units must be periodically shut down and deposits removed or the units replaced. Such fouling of heat exchangers, and also such equipment as furnaces, pipes, reboilers, condensers, compressors, auxiliary equipment, and the like, is costly by reason of the loss of production time and the man hours required for disassembly, cleaning and reassembly of unit process equipment components. The equipment is usually fabricated of carbon steel, stainless steel, or aluminum.
The fouling is generally attributed to the presence of unstable components, such as oxidized derivatives of hydrocarbons, the inorganic impurities present in hydrocarbon fractions, the presence of olefinic unsaturated hydrocarbons or their polymeric derivatives, or the like. Thus, almost all crude oil and fractions thereof, as well as process cuts prepared from such, contain minor amounts of readily oxidized and oxidizable hyrdocarbon constituents. Furthermore, almost all crude oil contains small amounts of dissolved oxygen, sulfur and metals, in a free and/or chemically combined state. If chemical and/or thermol treatment is involved, the olefinic substitutes may be polymerized.
The use of certain organophosphorous compounds as antifoulant additives to mineral hydrocarbon mixtures employed as refinery feedstocks has heretofore been proposed. Thus, Newkirk, and Miller in U.S. Pat. No. 3,261,774 teach the addition of various N-alklyl amidophosphoric acids as antifoulants, and Gillespie and Ryer in U.S. Pat. No. 3,558,470 teach the addition of mixtures of (I) organophosphite esters and (II) a condensation product of mono-, or di, carboxylic acid or anhydride thereof with a polyalkylene polyamine or the reaction product of I with II. Gillespie et al never use only phosphite esters as additives.
So far as known to us, no one has heretofore ever employed only mono and di phosphate or phosphite esters and amine salts thereof as antifoulant additives in crude oil materials. Such phosphorous esters, and amine salts thereof, have now been found characteristically to display surprising and very useful antifoulant activity in crude oil materials. Not only do these materials inhibit and suppress and even prevent, fouling when in crude oil materials, but also they unexpectedly appear to reduce the fouling in previously used and fouled crude oil refinery processing quipment. Such additives in combination can be considered to be arguable synergistic in some of these effects, and applications, as those skilled in the art will appreciate. The art of reducing fouling in refining streams is very complex and the reasons why a particular antifoulant system works to reduce fouling effectively in some mineral hydrocarbon mixtures, but perhaps not in others, are not now known.